1. Field of the Invention
The present invention relates to a barrier film substrate having excellent gas-barrier capability. More precisely, the invention relates to a barrier film substrate favorably usable in various organic devices such as image display devices, in particular, to a barrier film substrate useful as a substrate for flexible organic electroluminescent devices (hereinafter referred to as “organic EL devices”) and to a method for producing it, and also to an organic device.
2. Description of the Related Art
Heretofore, a barrier film laminate fabricated by forming a thin metal oxide film of aluminium oxide, magnesium oxide, silicon oxide or the like on the surface of a plastic substrate or a film is widely used for wrapping or packaging articles that require shielding from various gases such as water vapor or oxygen and for wrapping or packaging edibles, industrial articles and medicines for preventing them from being deteriorated. Apart from its applications for wrapping and packaging articles, in addition, the barrier film substrate is being used in liquid-crystal display devices, solar cells and EL devices.
In recent development of image display devices such as liquid-crystal display devices and EL devices, the transparent substrate to constitute these devices is required to be lightweight and has a large panel size and, in addition, it is further required to satisfy high-level requirements in that it has long-term reliability and has a lot of latitude in designing its shape and that it enables curved-face display. For the transparent substrate capable of satisfying such high-level requirements, a plastic substrate is being used as a new type of substrate substitutable for a conventional glass substrate that is heavy and readily cracked or broken and hardly worked into a large-size panel. Not only satisfying the above requirements, but also the plastic substrate is applicable to a roll-to-roll system, and therefore it is more advantageous than a glass substrate in that the producibility with it is high and the production cost with it is low.
However, the film substrate of transparent plastics or the like is problematic in that its gas-barrier property is inferior to that of a glass substrate. When a substrate having a poor gas-barrier property is used, water vapor and air may penetrate through it; and, for example, when it is used in liquid-crystal display devices, the liquid crystal in the liquid-crystal cell may be degraded and the degraded part may be a display failure, thereby worsening the display quality of the devices. For solving the problem, a barrier film substrate that comprises a thin metal oxide film formed on a film substrate has been developed. For example, as a barrier film substrate for use in wrapping materials and liquid-crystal display devices, there are known a plastic film coated with silicon oxide through vapor deposition (see JP-B 53-12953), and a plastic film coated with aluminium oxide through vapor deposition (see JP-A 58-217344). These have a water-vapor barrier level of 1 g/m2/day or so.
However, large-panel liquid-crystal display devices and high-definition display devices developed these days require plastic film substrates having a further improved gas-barrier capability, for example, having a water vapor permeability of at most 0.1 g/m2/day or so. Further recently, the development of organic EL display devices and high-definition color liquid-crystal display devices is being more promoted, and they require transparent substrates having a further improved barrier capability (especially having a water vapor permeability of less than 0.01 g/m2/day). To satisfy these requirements, some methods expected to produce a higher barrier level have been investigated, for example, a sputtering method of forming a thin film by the use of a plasma generated through glow discharge under low pressure, and a CVD method for film formation. In addition, also proposed is an organic light-emitting device provided with a barrier film having an alternate laminate structure of organic layer/inorganic layer fabricated according to a vacuum evaporation method (see U.S. Pat. No. 6,268,695 (page 4 [2-5] to page 5 [4-49])). Further, for giving the necessary folding resistance enough for application to flexible image displays to a plastic film, disclosed is a technique of using a polymer formed through polymerization of an acrylic monomer and having a volume shrinkage of less than 10% as an organic layer of the film (see JP-A 2003-53881 (page 3 [0006] to page 4 [0008])).
However, for use for flexible organic EL device substrates, they are still unsatisfactory in point of the adhesion between the organic layer/inorganic layer, and further improving them is desired. Given that situation, taken is a trial of using a resin crosslinked with a diacrylate having, as a polar group, an ether group as the organic layer thereby improving the adhesiveness of the organic layer to the inorganic layer to be laminated thereon (see JP-A 2004-9395 (page 3 [0005] to page 4 [0008], page 7 [0017] to [0022])); however, this is still insufficient in point of the gas-barrier capability necessary for organic EL devices.